Process for providing rust free surfaces on ferrous metal parts



Patented Oct. 7, 1947 PROCESS FOR PROVmING RUST FREE SUR- FACES ON FERBOUS METAL PARTS Max Frazer, Philadelphia, Pa.

No Drawing. Application September 21, 1944, Serial as. 555,160

3 Claims: (Cl. 134-2) (Granted under the act of March 3, 1883, as amended April 30, 1928: 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to a process especially useful for removing rust from and for rust proofing small fabricated steel parts, such as small steel machine screws, small steel gears, small steel pinions, small steel levers, small steel spindles with and without shoulders thereon, small thin steel plates of various shapes and other small parts of steel or ferrifercus metals of complicated shape or configuration which may or do form part of assemblies which are themselves comparatively small, such as watches, mechanical time fuzes for projectiles, and small composite units of other assemblies in which precision of action is desirable or necessary.

' The small ferrous metal parts referred to above are of the type which are produced by machine tools in comparatively large quantities once it has been determined that such parts are to be produced. The parts, as will be appreciated, are of such small dimensions that many thousands of them may be contained in a comparatively small box or container. In order that the smallness of the parts under consideration may be i fully appreciated, a few examples of such partsare given as follows: machine screws one-eighth inch long and of a diameter must less than their length, and provided with very small pitch threads; small gears, for example, three-eighths inch in diameter with small teeth of less than one-sixteenth inch pitch; small spindles, for example, one-half inch long of three-thirty-seconds inch diameter with reduced ends and shoulders at the base of such reduced ends. It is to be understood, however, that the process is not conlined in application to these specifically named parts, which are merely given as illustrative of the subject to which the process may be applied. Hereinafter, the subject matter to which the inventlon is especially applicable is referred to as small ferrous metal parts, without any intention of limitation to any particular or special small part; and the term "ferrous metal" is intended to include iron, steel or other metal or alloy containing iron in such amount that rusting thereof may occur.

When small ferrous metal parts are stored or kept before use, they are not usually stored or kept as individual elements apart from each other, but many hundreds or thousands of them, according to their sizes, are often placed together in a single container, box or carton. Due to atmospheric influences. moisture, changes in tem- 2', 4 erature and relative humidity, electrolytic eflects and possibly other causes which include strains and deformations in the metal of the parts, andassembling the parts in positions or localities" intended or work free from the part during use and such disengaged rust in an assembly where precision of action is desired may seriously ad versely affect the action of the assembly. For example, rusty parts or particles of free or disengaged rust in a mechanical time fuse for a. projectile may cause undesired delays or other,

malfunctioning in the action of the fuse.

It will be appreciated also that any rust on such small or fine parts is also objectionable because the rust on the small parts produces comparatively large efiects of increased friction or dimensions interfering with proper functioning of the part; and the rust acting cathodically with respect to the steel or ferrous metal part may accelerate or cause further rusting.

The satisfactory removal of rust from small ferrous metal parts has not heretofore proven to be simple of accomplishment. and many tests and experiments were necessary before a satisfactory process was finally discovered. An essential requirement of a rust removing process for small ferrous metal parts intended for use in assemblies where precision of action is essential is that the rust removing process shall not change or affect. or materially change or aflect, the surface finish of the metal part. For example, small steel screws are usually finished with a bright or shiny metal finish characteristic of the freshly cut metal, and spots or areas of rust that may later form thereon must be removed without destroying or materially altering this bright finish. A further essential requirement of a rust removal and rust preventing process is that once the process has effectively and satisfactorily removed the rust without impairment of the finish of the metal part or parts, the part or parts must be effectlveiy protected, against further rusting or impairment of finish.

Still another essential requirement of an effective rust removal and rust preventing process is that water or water moisture must be so effectively removed from the part after removal of the rust therefrom that rusting due to ineffective removal of water or water moisture does not take place. Heatin the parts, especially small parts, with some rusting, unless special measures are applied 5 as in the present invention.

Removing rust from small ferrous metal parts or drying small metal parts by tumbling them in fine sawdust, for example, fine hardwood sawdust, ls not very efl'ective in either removing rust .10

from or in drying small metal parts which have a complicated shapes. small recesses or small indentations which, for example. are found in fine threaded small screws, and fine toothed small of such solutions; (5) rinsing or washing with water, preferably first with hot water and then with cold water; (6) submerging the parts in a water solution of sodium nitrite which has been rendered alkaline; (7) intimate contact or treatment of the parts with an emulsion of a so-called "soluble oil, namely a mixture of a substantially neutral non-drying oil and an emulsifying agent;

(8) removal of excess of oil emulsion by mechanical action, for example, centriiugally, accompanied by removal of water by warm or hot air; (9) and finally applying to the parts a coating of an oil or oily material which has rust preventing properties.

gears, pinions and racks. Tumbling in sawdustgff act; only on areas accessible to the sawdust, and

I submerging the parts in the liquids contained in as a consequence the rust removal and drying is accomplished only at the outermost or more accessible surfaces. The action of the sawdust does not appear to extend, for instance, into deeper portions of recesses or completely between fine threads and line gears or teeth.

The process according to the present invention fulfills these essential requirements and effectively removes rust from small ferrous metal parts and prevents or inhibits further rusting of the parts. While the present process finds distinctive application in removal of rust from, and in the prevention of rusting of, small ferrous metal parts, it is to be understood that the process is also applicable to the treatment of large fabricated metal parts for removing rust therefrom and for protecting them against further rusting. This is one of the unique advantages of the present process, for it heretofore has been shown by experience, that a process which is suitable for removing rust from large parts and for protecting these against further rusting may not be suitable for use in connection with the treatment of small ferrous metal parts. teeth, threads or other cavities seem to stand in a diiferent category of materials from large parts so far as rust removal and rust prevention is concerned, particularly where the bright finish Small parts with fine 4 The treatment of the parts with the various 'liquid agents may be accomplished by dipping or separate containers, or the liquids may be sprayed or flowed over the parts. The small ferrous parts are advantageously treated in batches, each batch being subjected in succession to the treating steps indicated herein, or the process may be applied in a continuous manner by spraying the various liquids upon the parts at stations as the parts are moved by suitable conveying means past the statlons. The treatment of the parts in batches is described herein in detail as illustrative of the invention.

The first step of degreasing of the small forrous metal parts with an organic solvent for grease or oil is accomplished by submerging the batch of parts in an organic solvent for grease and oil and then stirring or agitating the parts therein. A suitable organic solvent that may be 85 used is trichlorethyiene, but it is to be understood that any other non-corrosive solvent for grease or oil may be used. Finished ferrous metal parts usually have a greasy surface due to mineral oils or other oils thereon, and it is necessary to re- 0 move such oil or grease before the application or metal luster of the part treated is to be preserved as much as possible in those localities where rusting has not occurred. Of course, here it is to be appreciated that where a rust spot or area of rust occurs the metal finish at those points has been impaired, as the one of the present invention, may remove this rust without substantial impairment of the bright finish of the metal surface which has not rusted, it cannot restore the original surface finish that has been removed by the rusting, since where rusting has occurred actual removal of metal or pitting of the metal has occurred. However, the present proccss does cause considerable brightening of the places where rusting has taken place.

and while a process,

The process according to the present invention comprises the following steps, applied in the order given, some of which, however, may be omitted as hereinafter explained: (I) degreasing the small ferrous metal parts with a suitable organic solvent for grease or oil such as trichlorethylene; (2) degreasing and cleaning with an aqueous alkaline solution; (3) washing or rinsing with water, preferably hot water, to remove alkaline solution; (4) subjecting the parts then to the 7 action of a hot water solution which removes rust from the metal part without attacking or destroying the bright metal finish of the metal, aqueous solutions of ammonium citrate and of the ammonium salt of tartaric acid being examples of aqueous chemical agents. Where the parts to be treated are not very greasy or oily, this step may be omitted, and especially where the following step of treatment with an aqueous alkaline solution effectively removes the grease or oil from the parts. Herein degreasing is also intended to include the removal of oil from the parts treated.

The step of degreasing the parts with an aqueous alkaline solution may be accomplished by submerging the parts for about two to six minutes in a 2 to 10% water solution of sodium or potassium hydroxide containing a surface tension depressant or emulsifying agent, the solution preferably being heated to from 185' F. to boiling, and stirring or agitating the parts in the solution. An aqueous alkaline solution. which is especially useful in practicing the invention, may be prepared by dissolving in each gallon of water 2 to 4 ounces of the following mixture: sodium orthosilicate (Na4SiOl), and 5% of a surfaceactive agent, advantageously of the sulphonate type compatible with an alkaline aqueous medium. An example of such a surface-active agent that can be used successfully for this purpose is sodium alkyl aryl sulphonate. This solution is used hot, preferably 135 F. to boiling, and the parts are submerged and agitated therein for two to six minutes or longer depending upon the extent of their greasiness.

Following the step of treating the parts with the aqueous alkaline solution. the parts are washed with hot water by submerging the parts in fresh running water at a temperature of from to 212 F. to remove alkaline solution from accomplish rust removal.

the parts. The parts are stirred or agitated in the water to assist in this removal.

After the washing step with water just described has been completed. the parts are submerged in a to water solution of amwithout destroying the brightness or bright metal appearance of the parts and without detrimentally affecting the dimensions of the parts. It has been found to be advantageous to incorporate preferably one that is stable and active both in the presence of acids and alkalies. The sodium salts of the so called sulphated or sulphonated' higher alcohols may be used as surface tension :depressants in the ammonium citrate solution.

From 0.03 to 0.50% of such a sulphated higher alcohol may be incorporated in the ammonium citrate solution.

After the parts have been treated with the ammonium citrate solution as above described, the parts are thoroughly washed with Water, preferably hot running water to thoroughly remove ammonium citrate and iron citrate from the parts.

After the last mentioned washing of the parts, the parts are advantageously submerged in a dilute water solution of sodium nitrite, for example, a 0.10% solution, adjusted to a pH of from 9 to 11.3 with sodium hydroxide or sulphuric acid. The parts may be allowed to remain in this solution from i to 3 minutes or much longer. Such a solution of sodium nitrite prevents rusting of the parts while they are in said solution. The parts are advantageously agitated in the solution to thoroughly contact the parts with the solution. This step, however, may be omitted when the parts are subjected to the next step described below, immediately after the preceding washing step. This sodium nitrite solution, therefore, serves as a resting or storage station for the parts after the rust is removed from them, and as such has proved to be a convenient medium. Its omission of course means that no time can be lost between the preceding water wash or rinse and the next step of treatment with a substantially neutral oil emulsion.

The next step of the process consists in submerging the parts in an emulsion of a so-called "soluble oil," for example, a neutral medium-viscosity mineral oil containing a dispersing or emulsifying agent, which causes the mineral oil when intimately mixed with water to form an emulsion. Such soluble oils are well known and need not be described in detail here. The emulsion used is preferably a fairly concentrated one and may consist of one part oi water and one part of soluble oil. The steel or ferrous metal parts are preferentially wetted by the oil particles of the emulsion, so that upon contact of the water wet parts with the emulsion of soluble oil a film of oil is formed directly upon the metal of the parts and on the walls of the crevices orrecesses thereof and displaces water from the parts. The surfaces of the parts are now enveloped by a. film of oil adhering to the metal surfaces and water has been removed from direct contact with the metal surfaces. During this step the parts are thoroughly agitated or stirred in the emulsion, which is advantageously heated to a temperature of from to E. so as to assure the formation of the water excluding film, of oil. Usually a treat- .ment of three minutes according to this stepis sufficient. Other materials may be used for the above described purpose instead of a soluble oil.

For example, .triethanclamine oleate may be used as the emulsifying agent for a medium viscosity mineral oil to iorman emulsion for this step of the process.

The parts are now removed from the emulsion and transferred to the rotating basket of a centrifugal drier to remove the excess of emulsion adhering to the parts. During the spinning of the parts in the centrifugal drier. warm or hot air may beblown over and through the parts to remove water which adheres as such or asan emulsion on the exterior of the oil films covering the metal parts. Because of the presence of the said film of oil on the metal of the parts, warm or hot air may be used to evaporate the water from the parts. The said films of oil prevent the warm air and water vapor from making direct contact with the metal parts, so that oxidation or rusting of the parts by the warm air and moisture does not take place. Were it not for the presence of said film, it would be impossible to dry the small parts with the warm air without some rusting occurring. This film of oil on the parts has a further distinct advantage in that it prepares the parts for reception of the coating of oily rustproofing agent applied to the parts in the next step of the process.

The parts, after drying and removal from the centrifugal drier, are submerged in thin or thinned slushing oil or compound or other rust preventing oil. Any good slushing oil or rust preventing compound may be used, and if its viscosity is too great to result in thin coating of the parts after removal therefrom, it is thinned with kerosene or mineral spirits. The thin layer of oil which is produced upon the parts by treatment with the soluble oil" emulsion, as described above, greatly facilitates the even and uniform application of the slushing oil or other rust preventing oil in this step of the process. The parts are stirred or agitated in the rust preventing oil for a few minutes, then removed and the rust preventing oil allowed to drain therefrom while being supported on a foraminous support. such as a wire screen or basket. Slushing oils in gen era] are oils or greases, usually containing two or more components in admixture which are known in the art and used for forming rust inhibiting coating on metal surfaces. The coating produced by them is oily and greasy. substantially nondrying, non-acidic and resistant to oxidation.

Ferrous metal parts sometimes have attached to them brass or other non-ferrous metal parts. An instance of this is to be found in the case of a brass gear with a steel pinion attached to it concentrically. The ferrous metal part in this case is nevertheless capable of treatment according to the present invention because the various steps of the present invention do not affect or corrode the brass. If it is desired to remove corrosion from both the brass and the steel of the part, the part may be first subjected to a treatment to remove corrosion from the brass and then the part treated in accordance with the present invention to remove the rust from the steel.

I claim:

1. A process for providing rust iree suriaces on ferrous metal parts which comprises subjecting said parts to an aqueous rust removing solution oi ammonium citrate. washing said solution from said parts. submerging said parts in a dilute aqueous solution'oi sodium nitrite. transierring said parts to a soluble oil emulsion containing an emulsifying agent whereby the water on said parts is displaced by said oil, removing the excess of emulsion adhering to said parts, and then evaporating the water from said parts.

2. A process for providing rust i'ree surfaces on ferrous metal parts which comprises subjecting said parts to an aqueous rust removing solution of ammonium tartrate, washing said solution from said parts, submerging said parts in a dilute aqueous solution 01' sodium nitrite. transferring said parts to a soluble oil emulsion containing an emulsiiying agent whereby the water on said parts is displaced by said oil, removing the excess of emulsion adhering to said parts," and then evaporating the water from said parts.

3. A process for providing rust iree surfaces on ferrous metal parts which comprises subiecting said parts to an aqueous rust removing solution 8 or an ammonium salt or a. polycarboxylic alkaue acid selected from the group including ammonium citrate and ammonium tartrate, washing said solution from said parts, submersing said parts in a dilute aqueous solution of sodium.nitrite, transferring said parts to a soluble oil emulsion containing an emulsifying agent whereby the water on said parts is displaced by said oil, removing the excess of emulsion adhering to said parts, and then evaporating the water from said MAX mom REFERENCES CITED The following references are of record in the his oi this patent:

UNITED STATES PATENTS Number Name Date amazes Shoemaker Mar. so, 194: 2,032,174 Johnson Feb.25, 1938 2,243,853 Castner Jan. 3, 1941 FOREIGN PATENTS Number Country Date 333,856 Great Britain Nov. 24, 1932 428,844 France Sept. 8, lflli 

